Abstract: An apparatus for controlling the opacity of a liquid-crystal window, having a light emitter positioned adjacent to one side of the liquid-crystal window, a light detector positioned adjacent to the opposite side of the liquid-crystal window, and a differential amplifier/driver that compares the output of the light detector with an input control signal and generates a differential drive signal to vary the opacity of said liquid-crystal window.

Abstract: Apparatus and method for visual-field testing. The apparatus includes an ocular device which fits over a subject's eye and which has a cavity-like inner surface dimensioned to encompass the subject's visual field. The ocular device is constructed to provide a background glow against which a fixed light image and a series of transient, different-position light image in the subject's visual field can be perceived. The images are preferably formed by a Badal-optical system which allows the images to be perceived without the need for corrective lenses. Also disclosed is a tandem-optics system for coordinately focusing fixed- and movable-position light image assemblies.